Yes, 200mm disc on mine.
Checked what? Seems unlikely there would only be one used over a nearly 9 year model range. I've seen at least 3 different versions...
Very well could be? Mine is a lightened A15 flywheel, and was factory drilled for the 200mm clutch.

The 63A does indeed match all the big ones, all of the others A-series transmissions do not.
The main reason I used a 63A is so I could more easily use a beefier clutch. At the time I was putting it together, no one made a stout clutch for the small spline transmissions.

Well, this has gone a bit off the original topic, so...
It sounds like to me your going to spend triple the money, break lots of unobtanium parts, and all just to make the same power as a stock CA/SR would. 😄

For what it's worth, my 1200 coupe has a fuel cell in the trunk. Never had an issue with vapors. Honestly, just about every 510 I've ever owned had fuel vapor problems and that's a more substantial barrier between driver and tank than my 1200.
If your tank is sealed well, and vents to the outside of the car (as mine does), I wouldn't be too worried about it. Those vapors are going to take the path of least resistance, which should be your vent tube.

Put about 20 miles on it today and ended up just driving it to my house instead of back to the shop. The few little things it needs I can fix at home, and this means I can take it out more often to do shake down runs since I'm only at the shop twice a week and need to spend my time there more productively than just cruising around in my car... 😋
Definitely need to get the wheels balanced soon as over 55mph they vibrate a bit. Will probably do that in the next week or two. 👍
Also need to tune the carbs as it's a bit rich...
And maybe change the thermostat since today it never got over 170F (it has a 160F thermostat in it)...